The present invention relates to an infusion rate adjusting device for drug solution injectors used for injecting a very small quantity of a drug solution such as, for example, an anesthetic agent, or an analgetic agent or antibiotic agent contained in a reservoir, into a patient""s body under the action of an external force such as a contractile force of elastic materials with rubberlike elasticity, expansion force of springs, or a pushing force due to a negative pressure chamber.
The drug solution injectors have been used for injecting a very small amount of a drug solution contained in a vial into a patient""s body by applying a contractile force of an elastic material having rubber-like elasticity on a reservoir for drug solution. In such injectors of the prior art, a fine tube has been used to infuse the drug solution into the body and the infusion rate of the drug solution is adjusted by a resistance of passage which varies with an internal diameter and length of the fine tube. This makes it possible to adjust the infusion rate to a desired value by adjustment of the internal diameter or length of the fine tube. For this reason, the drug solution injectors are marketed in combination of one fine tube per a reservoir.
In recent years, however, some cases need to change the infusion rate during infusion of the drug solution according to changes of the patient""s condition. In order to change the infusion rate during infusion of the drug soluiton, some flow rate control devices have been proposed in Japanese patent applications by Nissho Corporation. For example, JP-A-H9-280394 and JP-A-H10-28741 disclose a flow rate control device of the kind wherein plural fine tubes of different resistances of passages are respectively connected to a valve, and the flow rate of the drug solution is adjusted by changing over the valve. JP-A-H10-113386 discloses a flow rate control device of the kind wherein plural fine tubes are arranged in parallel and the flow rate of the drug solution is adjusted by opening or closing the fine tube with a clamp.
However, the above flow rate control devices have complex passages for the drug solution and are relatively difficult to operate setting of the inflow rate for the fine tube. On the other hand, the drug injectors of the kind wherein the force applied to the reservoir is reduced by the resistance of passage in the fine tube makes it possible to perform relatively fine adjustment at the accuracy of xc2x110%. However, the accuracy of the infusion rate is affected by tolerance of the internal diameter of the fine tube. Thus, the drug injectors using fine tubes of high precision result in high manufacturing cost.
In view of the above circumstances, the present invention has been made for the purpose of providing an infusion rate adjusting device for drug solution injectors, which is simple in operation to set out an infusion rate of the drug solution and which is considerably reduced in the manufacturing cost.
The present invention has been achieved on the basis of the idea that the above object is be achieved by arranging plural check valves of different opening pressures in a passage of a drug solution in series or in parallel so that the operator can select one of the check valves corresponding to a desired flow rate of the drug solution during infusion.
According to the present invention, there is provided an infusion rate adjusting device for drug solution injectors, which comprises a tubular flow control unit including plural check valves of different opening pressures, and means for selecting one of said check valves to adjust an infusion rate of the drug solution. In one preferred embodiment, the flow control unit includes plural check valves of a duck bill type, which are arranged in series and in descending order of opening pressures from the upstream side to the downstream side. In this case, it is preferred to use check valve selecting means including a tubular rod capable of being inserted into said check valve through a lumen of the flow control unit from the upstream side thereof to adjust the injection rate of the drug solution. The infusion rate of the drug solution is determined by the check valve which is not yet opened by the rod and is present in the upstream side of the lumen.
Preferably, the check valve selecting means including the rod is provided with a female engaging member having female engaging means and rotatably fitted on the rod, said female engaging means is adapted to be engaged with the male engaging means provided on the proximal end of the flow control unit so that the rod is linearly moved within the lumen of the flow control unit by rotating the female engaging member.
In another preferred embodiment, the flow control unit includes plural check valves of an umbrella type having different opening pressures arranged in series within a lumen of the tubular member. In this case, each of the check valves has a drug passage formed on its axis and, when the drug passage of one of the check valves is closed by said check valve selecting means, the check valve with the closed drug passage serves as the check valve which determines the injection rate. Preferably, such check valve selecting means serving as the passage closing means is provided the sidewall of the flow control unit.